JP5135849B2 - Gain control device, optical transmission device, and gain control method for optical amplifier - Google Patents

Description

  The present invention relates to a gain control device, an optical transmission device, and a gain control method for an optical amplifier, and in particular, a WDM (Wavelength) for providing a long distance by providing optical fiber amplifiers typified by an erbium-doped optical fiber amplifier (EDFA) in multiple stages. (Division Multiplex) The present invention relates to a technique suitable for use in an optical transmission system.

  2. Description of the Related Art In recent years, as an example of a WDM optical transmission system, a metro core system that can insert / drop (add / drop) an optical signal of an arbitrary wavelength at an arbitrary node connecting local base cities has attracted attention. FIG. 7 is a block diagram showing a configuration example of a metro core system. In the system shown in FIG. 7, an OADM node 100 as a plurality of optical transmission apparatuses is connected in a ring shape via a transmission line (optical fiber) 110. Each OADM node 110 inserts (adds) signal light of an arbitrary wavelength (channel) into the transmission path 110, or branches (drops) signal light of an arbitrary wavelength among WDM signal lights transmitted through the transmission path 110. ) And so on.

  Each OADM node 100 has a pre-amplifier 102a as a preamplifier and a post-amplifier as a post-amplifier appropriately provided in the front and rear stages of the OADM unit 101 together with the OADM unit 101 that branches and inserts signal light. An amplifying unit 102b (hereinafter referred to as an optical amplifying unit 102 if not distinguished) is provided, and through the amplifying action of these optical amplifying units 102, adjacent OADM nodes (hereinafter also simply referred to as “nodes”) 100 are provided. The transmission distance is increased by compensating for the loss of the signal light level between them.

  Furthermore, in the system in which signal light is added / dropped at an arbitrary node 100 in this way, the number of signal wavelengths transmitted through the system (transmission path 110) (hereinafter also referred to as the number of transmission wavelengths) dynamically changes. In order to keep the output optical power of each wavelength (channel) constant (maintaining gain flatness with respect to the wavelength) against the fluctuation in the number of wavelengths, the optical amplifying unit 102 normally has a constant gain control (AGC). An AGC amplifier 120 having a function is applied.

  Here, for example, as shown in FIG. 8, the AGC amplifier 120 is the light branched by the optical couplers 122 and 123 such as optical couplers and the optical couplers 122 and 123 that respectively branch part of the input / output light of the EDFA 121 and EDFA 121. And a constant gain control unit 126 for controlling the pumping light power to the EDFA 121 so that the power ratio monitored by the PDs 124 and 125 is constant. Configured. The EDFA 121 includes an EDF as an amplification medium (not shown), an excitation light source, and a multiplexing unit for supplying excitation light from the excitation light source from the front stage or the rear stage of the EDF.

  In the system shown in FIG. 7, for example, as shown in FIG. 9A, a large number (for example, 39 wavelengths) of optical signals are added from a certain node 100 (100A), and the next node 100 (100B) is added. Let us consider a situation in which another one-wave optical signal is added. In this situation, for example, as shown in FIG. 9B, when a failure such as dynamic reconstruction of the optical transmission path, human error, fiber cut, or connector disconnection occurs between the nodes 100A and 100B, the node 100B Only the added signal light remains (that is, the number of transmission wavelengths changes rapidly). At this time, for example, as shown in FIG. 10A, a phenomenon occurs in which the power level of the residual optical signal changes at the signal receiving end under the node 100 (100C).

For example, as shown in FIG. 16, the “signal receiving end” is an optical / electrical conversion (O) that receives the drop light branched at the node 100 (100C in FIG. 8A) and converts it into an electrical signal. / E) means an optical receiver 131 having a function, and the same applies to the following description. The “signal transmission end” means an optical transmitter 132 having an electrical / optical conversion function (E / O) for converting a transmission signal (electric signal) into an optical signal. The optical signal node 100 (FIG. 9 (A) in 100A, 100B) from the optical transmitter 132 is inserted into the WDM signal light as an add light in.

Now, for example, as shown in FIG. 10B, the signal light power change mainly includes three factors: (1) spectral hole burning (SHB), (2) gain (wavelength) deviation, and (3 ) Some are due to Stimulated Raman Scattering (SRS) effect. Each will be described below.
(1) SHB
The first factor, SHB, is a physical phenomenon that occurs when optical amplification is performed in an optical amplifier such as the EDFA 121, and is characterized in that the optical signal power on the short wavelength side is reduced. That is, for example, as shown in FIG. 11, when an optical signal of one wave (for example, 1538 nm) of C band (1530 to 1565 nm) is amplified in the EDFA 121, the EDFA gain in the vicinity of the signal wavelength decreases (this is called a main hall). ) And the EDFA gain near 1530 nm also decreases (this is called a second hole).

In the C band, the main hole is deeper at the shorter wavelength side (the gain reduction amount is larger), and both the main hole and the second hole are deeper as the optical signal input power is higher. Such SHB is averaged in a state where multi-wavelength signal light is input, and thus the influence thereof is small. However, the influence increases as the number of input wavelengths decreases.
Therefore, for example, as shown in the column (1) in FIG. 10B and FIG. 12A, a signal having a wavelength inserted from the node 100A because a failure has occurred between the nodes 100A and 100B as described above. When light is lost and only signal light having a wavelength inserted at the node 100B remains (see time t0 in FIG. 10A), the gain of the EDFA 121 forming the post-amplifying unit 102b in the node 100B is short. As the residual signal light on the wavelength side decreases (−ΔP), a phenomenon occurs in which the output light power also decreases.

  In the example shown in the column (1) in FIG. 10B, one wave λa and the long wavelength band L (inserted at the node 100B) remain, but arranged at a wavelength longer than λa. When the intermediate wavelength band M (inserted at the node 100A) is lost, the output light power of the signal light having the remaining wavelength λa on the short wavelength side as compared with the output light power in the wavelength band L on the long wavelength side Shows a drop of ΔP.

  As described above, it is known that the influence of the SHB received by the remaining signal light after the change when the wavelength band amplified by the optical amplifying unit 102 changes varies depending on the number of wavelengths of the remaining signal light and the arrangement thereof. Yes. In other words, the amount of gain variation in the optical amplifying unit 102 due to SHB changes according to the number of signal wavelengths and the arrangement. Note that details of SHB are described in Non-Patent Documents 1 to 3 below.

(2) Gain Deviation The second factor, gain (wavelength) deviation, is a phenomenon that occurs in the optical amplifying unit 102 (102a, 102b) configured as the AGC amplifier 120. That is, the optical amplifying unit 102 performs control (AGC) to keep the average gain of the signal light constant as described above, and when the wavelength having the deviation remains, the gain of the signal light is adjusted to the target gain. Therefore, for example, as shown in the column (2) in FIG. 10B, a change (in this case, + ΔP) occurs in the output optical power from the optical amplifying unit 102 for the residual optical signal. That is, in this case, the operating point in the optical amplifying unit 102 changes according to the number and arrangement of signal wavelengths, and the gain spectrum changes.

  Even before a failure occurs between the nodes 100A and 100B, even if a signal light of a uniform level is input in the signal light for each wavelength, the post-amplification as the AGC amplifier 120 in the node 100B In the unit 102b, the WDM signal light having the power distribution as shown on the left side of the column (2) is output from the EDFA 121 by the gain wavelength characteristic of the EDFA 121 (see FIG. 8). In the example shown in the column (2) in FIG. 10B, among the wavelength components of the WDM signal light amplified by the EDFA 121, the output power is smaller than the target output power for AGC control before the failure occurs. The case where the wavelength λb remains when a failure occurs is shown.

  That is, when AGC control is being performed, due to a failure occurring between the nodes 100A and 100B, all the wavelength bands B other than λb (inserted by the node 100A) are lost, while being inserted by the node 100B. In the post-amplification unit 102b of the node 100B, the target gain (operating point) is increased by the constant gain control unit 126, and the remaining wavelength band λb. The optical power after amplification of the signal light is obtained as the target of AGC control. Therefore, in the case of the signal light having the wavelength λb, it increases by ΔP compared to before the wavelength arrangement fluctuates.

(3) SRS effect The third factor, the SRS effect, is a phenomenon that occurs in the transmission line 110 (see FIG. 7). An optical amplifier using the SRS effect is a Raman amplifier. For example, as shown in FIG. 13, the SRS of a general single mode fiber has a characteristic that it has a gain peak on the low frequency side of about 13 THz from the pumping light wavelength (about 100 nm long wavelength side when the pumping light wavelength is near 1400 nm). Therefore, optical signal amplification in an arbitrary wavelength band is possible by selecting the pumping light wavelength. However, as shown in FIG. 13, amplification at the pinpoint wavelength is not possible, and the amplification (gain) characteristic has a certain extent with respect to the wavelength. An amplification phenomenon occurs.

  That is, when a WDM optical signal is transmitted through the transmission line 110, the signal light power on the short wavelength side becomes the pumping light power, and the signal light on the long wavelength side is amplified. As a result, as shown in FIG. 14, a phenomenon occurs in which the signal light power increases toward the longer wavelength side. Therefore, as described above, when a failure occurs between the nodes 100A and 100B and only one wavelength of signal light remains, as shown in the column (3) and FIG. 12B in FIG. As the residual signal light becomes smaller, the power cannot be taken from the shorter wavelength side, resulting in a decrease in power (gain) (−ΔP). That is, the effect of SRS changes according to the number and arrangement of signal wavelengths.

  As described above, when the number of wavelengths of the WDM signal light transmitted through the transmission line 110 fluctuates greatly, the output optical power of the residual signal light (residual channel) is affected by the effects of SHB, gain deviation and SRS as described above. Change. In the OADM unit 101, it is possible to provide a function of adjusting the level of the signal light of each wavelength by feedback control. By such feedback control, the output light power can be changed due to the above-described variation in the number of signal light wavelengths and the arrangement. Can respond.

  However, such feedback control corresponding to each wavelength is normally performed after the number of wavelengths fluctuates (time point t0) until it functions constantly (see time t2), as illustrated in FIG. 10A. It takes a considerable amount of time. Therefore, it is practically difficult to suppress transient fluctuations in output light power after the number of wavelengths fluctuates as shown at time t1 in FIG.

  Such a transient fluctuation of the output light level is a system in which optical amplifiers 102 that perform the same AGC are provided in multiple stages even if the amount of change per node 100 and each transmission line 110 is not so large. The characteristics of power fluctuations generated in one optical amplifier 102 are accumulated. For example, as shown in FIG. 15, the negative side output optical power change (−ΔP) per channel generated in each optical amplifying unit 102 and transmission line 110 is caused by an increase in the number of spans, that is, an increase in the number of stages of optical amplifiers passing therethrough. It will be accumulated. The example of FIG. 15 shows that the negative side output power fluctuation increases with an increase in the number of spans.

  In conventional optical transmission systems where the transmission distance is short and the number of stages of optical amplifiers is small, this fluctuation is small and has not been a problem. However, if the number of optical amplifier stages increases as the system becomes longer in the future, this figure As shown in FIG. 15, the optical signal power at the signal receiving end may exceed the allowable reception range, and a transmission error may occur. In other words, in a wavelength division multiplexing optical transmission system that is relayed and transmitted by a plurality of nodes 100 each having an OADM function, a failure in one transmission path section may affect communication in another transmission path section. There is.

In addition, as a technique related to the present invention, there are techniques described in Patent Documents 1 to 4 below.
Patent Documents 1 and 2 disclose that the number of transmission wavelengths is obtained by inputting a part of the signal light input to the optical amplifier as monitor light into a wavelength demultiplexer (DEMUX) and demultiplexing it for each wavelength. Is to count. Specifically, in the technique of Patent Document 1, the input light of the optical amplifier is monitored for each wavelength, and the attenuation amount of the variable optical attenuator provided at the output of the optical amplifier is changed according to the change in the monitored value and the number of wavelengths. Adjustment is performed to collectively control the output optical power. On the other hand, in the technique of Patent Document 2, in an optical amplifier in which optical amplification fibers such as EDF are connected in multiple stages, the signal light power and the number of wavelengths detected from the input light to the optical amplification fiber in the previous stage, and the light in the latter stage Adjusting the pumping light power to each optical amplifying fiber and the amount of attenuation of a variable optical attenuator provided between each optical amplifying fiber based on the signal light power detected from the output light of the amplifying fiber Thus, the gain and gain spectrum of the entire optical amplifier are controlled.

Further, as a technique for compensating (flattening) the above-described change in optical amplifier output (deviation of wavelength characteristics of signal light), a dynamic gain equalizer (DGEQ) and the following Patent Documents 3 and 4 are proposed. There are also technologies. The technique of Patent Document 3 includes an optical circulator, an optical reflector, a variable optical attenuator, and a WDM coupler, and performs gain equalization for each of a plurality of signal lights (wavelengths) demultiplexed by the WDM coupler. The technique of Patent Document 4 relates to a variable gain flattener having a plurality of gratings having a long-period structure and an adjustment unit (piezo converter and piezo control circuit) for adjusting an attenuation factor for each of the gratings. is there.
JP 2001-168841 A JP 2003-258348 A JP-A-10-173597 JP 11-337750 A Masato NISHIHARA, et.al., "Characterization and new numericalmodel of spectral hole burning in broadband eribium-doped fiber amplifier", 2003 Optical Society of America. Masato NISHIHARA, et.al., "Impact of spectral hole burning in multi-channel amplification of EDFA", 2004 Optical Society of America. Maxim Bolshtyansky, "Spectral Hole Burning in Erbium-Doped Fiber Amplifiers", JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL.21, NO.4, APLIL 2003.

  However, in the above-described level adjustment function in the OADM unit 101 and the technique described in Patent Document 3, the received WDM signal light is demultiplexed for each wavelength, and the optical power for each wavelength is obtained by a variable optical attenuator for each wavelength. Therefore, the scale of the apparatus increases and the cost increases. In particular, if an attempt is made to use a VOA that operates at a high speed in order to obtain a high-speed response characteristic, the VOA is expensive. Therefore, if only the number of wavelengths is prepared, the cost further increases. Moreover, the above-described transient fluctuations in the output optical power cannot be suppressed with a VOA that operates at a relatively low speed due to cost constraints.

Furthermore, the dynamic gain equalizer and above mentioned is a relatively slow response speed of about 30 ms, the cost is high and several hundred thousand yen, and there are problems such as the insertion loss is large (approximately to 5 dB) Therefore, introduction into the system is not realistic. In the technique disclosed in Patent Document 4, the attenuation rate of light transmitted through the grating by individually changing the characteristics of the plurality of gratings by changing the pressure applied to the grating by controlling the piezo converter by the piezo control circuit. However, since the physical control of the pressure change with respect to the grating is performed, the response speed is still low.

The techniques described in Patent Documents 1 and 2 do not suppress the transient fluctuation of the gain wavelength characteristic of the EDFA 121 due to the fluctuation of the number of wavelengths as described above, and consequently the transient fluctuation of the output light level.
The present invention has been devised in view of the above problems, and is intended to suppress the fluctuation of the output light power of the optical amplifier due to the fluctuation of the signal light level, particularly the fluctuation of the wavelength number of the wavelength multiplexed signal light, at high speed. Objective.

(1) Therefore, the gain control device of the present invention is a device for controlling the gain of an optical amplifier that amplifies the input wavelength multiplexed signal light, and the number of wavelengths of the wavelength multiplexed signal light is equal to or less than a set threshold value. When the characteristics of the output optical power fluctuation of the optical amplifier are acquired in advance , the fluctuation amount of the output optical power due to the change in the number of wavelengths compensates the characteristics based on the acquired characteristics of the output optical power fluctuation As the number of wavelengths of the wavelength multiplexed signal light decreases, the gain of the wavelength multiplexed signal light increases or the gain of the wavelength multiplexed signal light decreases as the number of wavelengths of the wavelength multiplexed signal light decreases. A target gain calculation unit that calculates one of the values obtained as a target gain of the optical amplifier, and for the optical amplifier to amplify the wavelength multiplexed signal light with the target gain calculated by the target gain calculation unit Control signal It is characterized in that and a control signal output unit for outputting.

The present invention is characterized by an optical amplifier in which the gain of signal light is increased or decreased as the number of wavelengths of wavelength multiplexed signal light is reduced. This is because the smaller the number of signal wavelengths after the change in the number of signal wavelengths, the greater the change in the total power, and the greater the amount of fluctuation in the output optical power when the number of signal wavelengths to be compensated changes.
The amount of gain increase / decrease at the wavelength number 1 as compared with the maximum number of wavelengths may be determined by SHB, gain deviation, and SRS which are the main factors of the transient output light power fluctuation described above. Thus, for example, if the present invention is applied to an optical amplifier arranged at each node, fluctuations in output optical power can be compensated for each node. Note that the amount of change in the increase or decrease in the signal light gain with respect to the number of wavelengths differs depending on not only the number of wavelengths but also the system condition of the signal wavelength band, the type of transmission path, and the like. This is because the fluctuation amount of the output optical power to be compensated for depends on such system conditions. Therefore, if the change amount of the increase or decrease of the signal light gain with respect to the number of wavelengths is made too small, the compensation of the output light power fluctuation amount becomes insufficient. On the other hand, if it is too large, depending on the wavelength condition of the change in the number of signal wavelengths, the input upper limit of the receiver may be exceeded and the transmission characteristics will be degraded. Therefore, grasp the characteristics of output optical power fluctuations at a small number of wavelengths in advance from the configuration of the optical transmission device applied as the optical amplifier and the characteristics of the applied wavelength multiplexing optical transmission system, and compensate for them. The minimum value necessary to do this is preferred. For example, if the output fluctuation occurring between the nodes is approximately <1 dB (less than 1 dB), the maximum amount of gain increase / decrease of the optical amplifier to which the present invention is applied is preferably approximately <1 dB (less than 1 dB). .

  It is preferable that the rate of change of the increase or decrease in the signal light gain with respect to the number of wavelengths changes steeply and continuously as the number of signal wavelengths decreases (FIGS. 2A and 2B). The reason is that when the gain is increased when the number of signal wavelengths is large, there is a problem such as an increase in the required pumping light power of the optical amplifier, and it is necessary to suppress the gain increase when the number of signal wavelengths is large as much as possible. Further, as the number of signal wavelengths decreases, the amount of fluctuation of the output optical power when the number of signal wavelengths changes continuously increases. Therefore, as shown in FIGS. 2A and 2B, the gain increase / decrease amount in the region where the number of wavelengths is small is continuously changed according to the number of signal wavelengths.

In the mode of increase (A1) to decrease (A2) in the signal light gain shown in FIGS. 2 (C) and 2 (D), the gain value G1 when the number of signal wavelengths is the maximum nmax is linear or saturated. Therefore, as compared with FIGS. 2A and 2B, the gain is increased when the number of signal wavelengths is large. This is not preferable because there is a problem of an increase in required pumping light power.
As a conventional example, there is Japanese Patent Application No. 11-256438 (Japanese Patent Laid-Open No. 2001-086071). When n (number of wavelengths) <nmax (maximum number of wavelengths), Pt (total output power)> Pmax (maximum total output power) × n / nmax is controlled to reduce the gain shortage of the existing channel due to the influence of channel increase / decrease This is an optical amplifier. From the above equation Pt> Pmax × n / nmax, Pt is set to a larger value at the number of wavelengths n than when nmax (maximum number of wavelengths) is indicated by an inequality sign, but the value of Pt is not dependent on the number of signal wavelengths. For example, when the number of wavelengths is n, n-1, n-2,..., Pt per signal light is substantially constant from the above equation Pt> Pmax × n / nmax. Therefore, Japanese Patent Application No. 11-256438 is different from the present invention, and the effect of accurately reducing the amount of gain increase / decrease when the number of channels fluctuates can be obtained while realizing the required pump light power reduction as in the present invention. Absent.

(2) Further, another gain control device of the present invention is a device that controls the gain of an optical amplifier that amplifies the input wavelength multiplexed signal light, and the number of wavelengths of the wavelength multiplexed signal light is a set threshold value. Is greater than the threshold value, a substantially constant gain value is calculated as the target gain of the optical amplifier. On the other hand, when the number of wavelengths of the wavelength multiplexed signal light is equal to or less than the threshold, the wavelength of the wavelength multiplexed signal light is calculated. When the number is equal to or less than the threshold, the output optical power fluctuation characteristic of the optical amplifier is acquired in advance , and the output optical power fluctuation amount due to the change in the number of wavelengths is based on the acquired output optical power fluctuation characteristic. The gain value of the wavelength multiplexed signal light is increased according to the number of wavelengths, or the gain value of the wavelength multiplexed signal light is decreased according to the number of wavelengths so that the fluctuation amount for compensating the characteristic is suppressed. One of the values A target gain calculation unit that calculates the target gain of the optical signal, and a control signal output unit that outputs a control signal to the optical amplifier to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculation unit; It is characterized by having
(3) Further, the target gain calculation unit is changed to a wavelength number information acquisition unit that acquires wavelength number information of the wavelength multiplexed signal light amplified by the optical amplifier, and the wavelength number information acquired by the wavelength number information acquisition unit. On the basis of this, a calculation unit for calculating the target gain in amplification by the optical amplifier may be provided.

(4) Further, the optical transmission apparatus of the present case includes a signal light processing unit that performs power adjustment on the signal light for each wavelength forming the wavelength multiplexed signal light to be transmitted in the wavelength multiplexing optical transmission system, and a front stage of the signal light processing unit. And / or an optical amplifier for amplifying the input wavelength-multiplexed signal light by pumping light and a gain control unit for controlling the gain of the optical amplifier, the gain control unit comprising the wavelength multiplexing When the number of wavelengths of signal light is equal to or less than a set threshold value, the characteristics of the output optical power fluctuation of the optical amplifier are acquired in advance , and the output due to the change in the number of wavelengths based on the acquired characteristics of the output optical power fluctuation as the variation amount of optical power is suppressed variation amount to compensate for the characteristics, the value the gain is increased in the smaller the number of wavelengths of wavelength multiplexed signal light wavelength multiplexed signal light or wave of the wavelength-multiplexed signal light, A target gain calculation unit that calculates a target gain of the optical amplifier as a target gain of the optical amplifier, and the wavelength division multiplexing with the target gain calculated by the target gain calculation unit. In order to amplify the signal light, a control signal output unit that outputs a control signal to the optical amplifier is provided.
(5) The target gain calculation unit, when the SN tolerance or input lower limit tolerance of the optical receiver optically connected to the wavelength division multiplexing optical transmission system is lower than a preset first threshold value, When the number of wavelengths is smaller, the gain of the wavelength multiplexed signal light is calculated so as to increase. When the input upper limit proof strength of the optical receiver is lower than a preset second threshold value, the number of wavelengths is small. It is also possible to calculate so that the gain of the wavelength multiplexed signal light is decreased.
(6) Furthermore, another optical transmission device of the present case includes a signal light processing unit that performs power adjustment on signal light for each wavelength forming wavelength multiplexed signal light to be transmitted in the wavelength multiplexing optical transmission system, and the signal light processing unit An optical amplifier for amplifying the input wavelength-multiplexed signal light with pumping light, and a gain control unit for controlling the gain of the optical amplifier, the gain control unit comprising: When the wavelength number of the wavelength multiplexed signal light is larger than a preset threshold value, a substantially constant gain value is calculated as the target gain of the optical amplifier, while the wavelength number of the wavelength multiplexed signal light is calculated as the threshold value. In the following cases, when the number of wavelengths of the wavelength multiplexed signal light is less than or equal to the threshold, the characteristics of the output optical power fluctuation of the optical amplifier is acquired in advance, based on the acquired characteristics of the output optical power fluctuation, Number of wavelengths As the amount of variation of the output optical power due to the change can be suppressed to a variation amount to compensate for the characteristics, values increased the gain value of the wavelength-multiplexed signal light in accordance with the number of the wavelengths or depending on the number of wavelengths, A target gain calculator that calculates one of the gain values of the wavelength multiplexed signal light as a target gain of the optical amplifier; and the wavelength multiplexed signal light with the target gain calculated by the target gain calculator And a control signal output unit for outputting a control signal to the optical amplifier.

(7) Further, the gain control method of the present optical amplifier is a control method for controlling the amplification gain of the optical amplifier that amplifies the input wavelength multiplexed signal light with the pumping light, and the number of wavelengths of the wavelength multiplexed signal light The characteristic of the output optical power fluctuation of the optical amplifier when is less than or equal to the set threshold is acquired in advance , and the amount of fluctuation of the output optical power due to the change in the number of wavelengths based on the acquired characteristic of the optical power fluctuation So that the amount of wavelength-multiplexed signal light gain decreases as the number of wavelengths of the wavelength-multiplexed signal light decreases, or the wavelength decreases as the number of wavelengths of the wavelength-multiplexed signal light decreases. One of the values obtained by reducing the gain of the multiplexed signal light is calculated as the target gain of the optical amplifier, and a control signal is output to the optical amplifier to amplify the wavelength multiplexed signal light with the calculated target gain. Do It is characterized by a door.
(8) Further, another gain control method of the present optical amplifier is a control method for controlling an amplification gain of an optical amplifier that amplifies an input wavelength multiplexed signal light with pumping light. When the number of wavelengths is greater than a preset threshold, a substantially constant gain value is calculated as the target gain of the optical amplifier, while when the number of wavelengths of the wavelength multiplexed signal light is equal to or less than the threshold When the number of wavelengths of the wavelength multiplexed signal light is equal to or less than the threshold, the characteristics of the output optical power fluctuation of the optical amplifier are acquired in advance , and the change in the number of wavelengths is based on the acquired characteristics of the output optical power fluctuation. A value obtained by increasing the gain value of the wavelength multiplexed signal light according to the number of wavelengths, or wavelength multiplexing depending on the number of wavelengths, so that the amount of fluctuation of the output optical power is suppressed to the amount of fluctuation compensating the characteristics. Decrease gain value of signal light One of the calculated values is calculated as a target gain of the optical amplifier, and a control signal is output to the optical amplifier in order to amplify the wavelength multiplexed signal light with the calculated target gain. .

  As described above, according to the present invention, the target gain calculation unit can suppress the fluctuation of the signal light level, particularly, the fluctuation of the output optical power of the optical amplifier due to the fluctuation of the number of wavelengths of the wavelength multiplexed signal light at high speed. Therefore, there is an advantage that the optical amplifier can be further multistaged and the transmission distance can be increased.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Note that the present invention is not limited to the following embodiments. In addition to the above-described object of the present invention, other technical problems, means for solving the technical problems, and operational effects will become apparent from the disclosure of the following embodiments.
[A] Description of an Embodiment of the Present Invention FIG. 1 is a diagram showing an optical transmission apparatus applied to a wavelength division multiplexing optical transmission system as an embodiment of the present invention. The optical transmission apparatus 1 according to the present embodiment can be connected in a ring shape via an optical transmission line 110 instead of the OADM node 100 shown in FIG. The optical transmission device 1 according to the present embodiment has the configuration of the front and rear optical amplifying units 10a and 10b as shown in FIG. 7 as compared to the optical transmission device 100 shown in FIG. 7 (see FIG. 8). ) Is different.

That is, the optical transmission device 1 according to the present embodiment has front and rear optical amplifying units 10a and 10b having configurations different from those shown in FIG. 7 (FIG. 8) (see reference numerals 102a, 102b, and 120). And an OADM unit 20 that is basically similar to that shown in FIG. 7 (see reference numeral 101).
Here, the pre-amplifier (optical amplifier) 10a as a preamplifier is input from the optical transmission device 1 (not shown in FIG. 1) connected to the upstream side, which is input via the optical transmission path 110. The wavelength multiplexed signal light is amplified and output to the OADM unit 20. The OADM unit 20 performs branching / adding processing on the wavelength multiplexed signal light from the pre-amplifier 10a and outputs the wavelength multiplexed signal light to be sent to the downstream optical transmission line 110 to the post-amplifier 10b. Further, the post-amplifier (optical amplifier) 10b as a post-amplifier amplifies the wavelength-division multiplexed signal light that has been subjected to the add / drop processing in the OADM unit 20 and outputs the amplified signal to the downstream optical transmission line 110.

  Therefore, the above-described OADM unit 20 is a signal light processing unit that performs processing on the signal light for each wavelength forming the wavelength multiplexed signal light to be transmitted in the wavelength multiplexed optical transmission system. The OADM unit 20 also has a level adjustment function in units of channels in addition to the function of performing branching / insertion processing, similar to that shown in FIG. 7 (see reference numeral 101).

  Further, both the above-mentioned pre-amplifier 10a and post-amplifier 10b have the same configuration, and the variation in the number of signal light wavelengths due to the occurrence of a fault as shown in FIG. Along with this, fluctuations in the output light power can be suppressed. Here, the pre-amplifier 10a and the post-amplifier 10b include an EDFA 11 as an optical amplifier that amplifies the wavelength-multiplexed signal light that is input by the pumping light, and controls the gain of the EDFA 11. A control unit (gain control device) 19 is provided. In the following description, the front optical amplification unit 10a and the rear optical amplification unit 10b are simply referred to as the optical amplification unit 10 unless they are distinguished from each other.

  The gain control unit 19 includes optical couplers 12 and 13, photodiodes 14 and 15, a wavelength number information acquisition unit 16, a calculation unit 17, and a control signal output unit 18. As described above, the EDFA 11 amplifies the input wavelength multiplexed signal light with the excitation light. The EDF as an amplification medium (not shown), the excitation light source, and the excitation light from the excitation light source in the signal light transmission direction of the EDF. An optical multiplexing unit for supplying from the upstream side (front stage) or the downstream side (back stage) is provided. The optical couplers 12 and 13 correspond to the optical couplers 122 and 123 shown in FIG. 8, respectively, and branch part of the wavelength multiplexed signal light that is input to and output from the optical amplifying unit 10.

  Further, the photodiode 14 outputs an electrical signal corresponding to the optical power of the wavelength multiplexed signal light input through the optical coupler 12, and is input to the EDFA 11 by this photodiode 14 (before amplification in the EDFA 11). ) The optical power of wavelength multiplexed signal light can be monitored. Similarly, the photodiode 15 outputs an electrical signal corresponding to the optical power of the wavelength multiplexed signal light input through the optical coupler 13, and is output from the EDFA 11 by this photodiode 15 (after amplification by the EDFA 11). The optical power of the wavelength division multiplexed signal light can be monitored.

  The wavelength number information acquisition unit 16 acquires wavelength number information of the wavelength multiplexed signal light amplified by the EDFA 11. Specifically, the number of wavelengths is counted by demultiplexing the branched light of the wavelength multiplexed signal light input to the EDFA 11 at a wavelength interval corresponding to the wavelength multiplexed channel and monitoring each of the demultiplexed lights. It has become. The configuration for acquiring the number of wavelengths in the wavelength number information acquisition unit 16 is also described in the above-mentioned Patent Document 1.

  The wavelength number information acquisition unit 16 acquires the wavelength number information from the branched light of the wavelength multiplexed signal light input to the EDFA 11. However, the wavelength number information acquisition unit 16 acquires the same from the wavelength multiplexed signal light output from the EDFA 11. Can do. Further, the signal may be acquired from a signal light monitoring function for each channel provided in the OADM unit 20. In this case, in the wavelength number information acquisition unit 16 in the pre-amplification unit 10a, the monitoring result of the signal light for each channel in the wavelength multiplexed signal light (before the add / drop processing) input to the OADM unit 20 The number of wavelengths information can be acquired. In addition, the wavelength number information acquisition unit 16 in the post-amplification unit 10b captures the monitoring result of the signal light for each channel in the wavelength multiplexed signal light (after the branching / insertion process) output from the OADM unit 20 to obtain the number of wavelengths. Information can be acquired.

Although some examples are given above, the means for obtaining the wavelength number information is not limited in the present invention.
In addition, the calculation unit 17 captures the monitoring result of the optical power of the wavelength multiplexed signal light input to the EDFA 11 from the photodiode 14 and is amplified by the EDFA 11 based on the wavelength number information acquired by the wavelength number information acquisition unit 16. The target gain corresponding to the number of wavelengths to be calculated is calculated. Specifically, as shown in FIG. 2 (A), in accordance with the number of wavelengths of wavelength-division multiplexed signal light, a gain value G1 having a maximum number of wavelengths is continuously increased exponentially according to the number of wavelengths. A value obtained by increasing (see dotted line A1 in FIG. 2A) or decreasing (see solid line A2 in FIG. 2A) the gain value so as to change the gain of the signal light is calculated as the target gain of EDFA 11. It is like that.

  Further, as shown in FIG. 2B, when the number of wavelengths of the wavelength multiplexed signal light is larger than the preset threshold value S or greater than or equal to the threshold value S, a substantially constant gain value G1 is set to the target of the EDFA 11. On the other hand, when the number of wavelengths of the wavelength multiplexed signal light is equal to or smaller than the threshold S or smaller than the threshold S, the gain value is increased according to the number of wavelengths (see the dotted line A1 in FIG. 2B) or The reduced value (see the solid line A2 in FIG. 2B) is calculated as the target gain of the EDFA 11.

Therefore, the above-described wavelength number information acquisition unit 16 and calculation unit 17 constitute a target gain calculation unit.
The threshold value S described above can be set to a number of about 25% or less of the total number of wavelengths that can be transmitted as wavelength multiplexed signal light in the wavelength division multiplexing optical transmission system.
The control signal output unit 18 outputs a control signal to the EDFA 11 so that the target gain calculated by the calculation unit 17 is obtained. Note that, like the control signal output unit 18 in the present embodiment, the EDFA 11 can also be subjected to automatic gain constant control (AGC control). In this case, the gain that is the target of the automatic gain constant control is received from the calculation unit 17. It is like that.

  The control signal output unit 18 monitors the optical power monitoring result of the wavelength multiplexed signal light input to the EDFA 11 from the photodiode 14 and the optical power monitoring result of the wavelength multiplexed signal light output from the EDFA 11 for the above-described AGC control. Are input from the photodiode 15 and are not shown in the EDFA 11 so that the input / output power ratio in the EDFA 11 that is an amplification gain for the wavelength multiplexed signal light in the EDFA 11 is the value calculated in the calculation unit 17. A control signal is output to drive the excitation light source.

  Since the AGC control is performed with the target gain calculated by the calculation unit 17 described above, wavelength multiplexed signal light consisting of about 25% or less of the number of channels that can be multiplexed in the wavelength multiplexing optical transmission system is transmitted. When the wavelength multiplexed signal light composed of a larger number of channels than the 25% is transmitted (when the wavelength is relatively large), it is output from the EDFA 11. The output light power of the signal light can be increased (see the upper part of FIG. 3C), or the output power of the signal light output from the EDFA 11 can be reduced (see the lower part of FIG. 3C).

  Conventionally, when performing AGC control of the gain of the EDFA, as shown in the “conventional” column of FIG. 3A, regardless of the number of wavelengths of wavelength multiplexed signal light (as described above, The gain given to the EDFA 11 is made constant even when the wavelength is relatively large. Therefore, if the above-described effects on SHB, gain deviation, and SRS are not taken into account, as shown in FIG. 3B, the output power is set to a constant gain. Japanese Patent Application Laid-Open No. 2000-232433 also describes controlling the EDFA in the same manner.

  However, as described above, since the demand for an increase in the number of spans and an increase in transmission distance in the wavelength division multiplexing optical communication system has been increasing in recent years, SHB, gain deviation can be provided in order to provide an optical amplifier configuration corresponding to this demand. There is a need to take into account the impact on SRS. Therefore, in the present embodiment, a substantially constant gain value G1 is calculated as the target gain of the EDFA 11 at the above-described relatively many wavelengths, while depending on the number of wavelengths at a relatively small number of wavelengths. A value obtained by increasing (see dotted line A1 in FIGS. 2A and 2B) or decreasing (see solid line A2 in FIGS. 2A and 2B) the gain value (output) of the signal light. Is calculated as a target gain of the EDFA 11.

  The magnitude of the influence of SHB, gain deviation, and SRS at the time of a small number of wavelengths on the output optical power fluctuation of the EDFA 11 constituting the optical transmission apparatus 1 depends on the characteristics of the wavelength multiplexing transmission system and the actual optical transmission apparatus. It varies depending on the configuration. Accordingly, the characteristics of the output optical power fluctuation at the time of a small number of wavelengths are grasped in advance from the configuration of the optical transmission apparatus 1 applied as the optical amplifying unit 10 and the characteristics of the applied wavelength division multiplexing optical transmission system.

Furthermore, for example, when the SN tolerance / input lower limit tolerance is poor as the characteristics of the receiver used in the system, it is preferable to control the gain (output) of the signal light in the direction of increasing. On the other hand, when the input upper limit proof strength is poor, it is preferable to control the gain (output) of the signal light in a decreasing direction.
Thereby, according to the grasped characteristic of the output optical power fluctuation at the time of the minority wavelength, the calculation unit 17 is a value at which the target gain value increases according to the number of wavelengths as shown in the upper part of FIG. As a calculation result, or as shown in the lower part of FIG. 3C, a value for decreasing the target gain value according to the number of wavelengths can be obtained as a calculation result. Can do.

  In the optical transmission device 1 in the wavelength division multiplexing optical transmission system configured as described above, the wavelength division multiplexed signal light input through the upstream optical transmission line 110 is amplified and input from the preamplifier 10a in the OADM unit 20. The wavelength multiplexed signal light is inserted / extracted for each channel, amplified by the post-amplifier 10b, and then transmitted to the downstream optical transmission line 110.

At this time, in the preamplifier 10a and the postamplifier 10b constituting the optical transmission apparatus 1, it can be generated depending on the number of wavelengths of the wavelength multiplexed signal light to be input (particularly noticeable when the number of wavelengths is relatively small). The fluctuation of the output optical power is suppressed through gain control according to the target gain calculated by the calculation unit 17 as follows.
That is, the wavelength number information income unit 16 that forms the gain control unit 19 of the optical amplification unit 10 acquires the wavelength number information of the wavelength multiplexed signal light that is amplified by the EDFA 11, and the wavelength that is input to the EDFA 11 by the calculation unit 17. The result of monitoring the power of the multiplexed signal light is taken in from the photodiode 14 (step A1 in FIG. 4).

  Referring to FIG. 2B as an example, in the calculation unit 17, the target gain (or target output power corresponding to the target gain) in amplification in the EDFA 11 based on the wavelength number information acquired by the wavelength number information acquisition unit 16. Is calculated (step A2). At this time, in the calculation unit 17, when the wavelength number acquired as information by the wavelength number information acquisition unit 16 is larger than or equal to the threshold value S shown in FIG. Therefore, a constant gain value G1 is calculated as a target gain. In the case where the number of wavelengths is equal to or less than the threshold value S shown in FIG. 2B or smaller than S, the gain (output) of the signal light of the EDFA 11 increases or decreases as the number of wavelengths decreases. Is calculated as a target gain.

  Then, the calculation unit 17 transmits the target gain value calculated as described above to the control signal output unit 18 (step A3), and the control signal output unit 18 operates the EDFA 11 with the target gain calculated by the calculation unit 17. In this manner, a control signal is output to the EDFA 11. If the number of wavelengths varies, a control signal is output to the EDFA 11 so as to change the gain of the EDFA 11 so as to obtain a target gain according to the number of wavelengths (step A4). Since the control signal output unit 18 of the present embodiment performs AGC control, the target gain calculated by the calculation unit 17 is a target of AGC control.

  For example, as shown in FIG. 9B, the upstream optical transmission line 110 or the upstream optical transmission is performed at the upstream side of its own optical transmission device 1 (reference numeral 100B shown in FIG. 9B). When a failure occurs in the apparatus 1 (reference numeral 100A shown in FIG. 9B), the wavelength multiplexed signal light transmitted from the upstream optical transmission apparatus 1 is lost, and therefore the optical transmission apparatus 1 itself. The number of wavelengths of the wavelength-division multiplexed signal light that is input to fluctuates.

Specifically, as shown in FIG. 5, in the own optical transmission device 1, the operation of inserting the signal light of wavelength λn from the upstream optical transmission device into the wavelength multiplexed signal light of wavelengths λ1 to λn-1 In the state (see the upper part of FIG. 5 ), when a failure occurs at the upstream side of the optical transmission device 1 as described above, the wavelength multiplexed signal light having the wavelengths λ1 to λn−1 from the upstream optical transmission device is generated. The input is cut off (see the lower part of FIG. 5 ).

  In the optical amplifying unit 10 according to the present embodiment, even when the number of wavelengths varies, when the number of wavelengths after variation is acquired by the wavelength number information acquiring unit 16, the EDFA 11 is used according to the acquired number of wavelengths. Therefore, the fluctuation in the output light power of the signal light, which has conventionally occurred, can be quickly suppressed along with such a fluctuation in the number of wavelengths.

  As described above, the level adjustment function in units of channels in the OADM unit 20 can follow the output level fluctuation at the time of wavelength fluctuation (t2 in FIG. 10A), but this level adjustment function alone. Then, there is a transition time that is substantially difficult to follow (t1 in FIG. 10A). In the optical transmission device 1 of the present embodiment, the level adjustment function in the OADM unit 20 and the gain control in the optical amplification unit 10 are also performed, and these cooperate to suppress power fluctuation.

Therefore, since the optical amplification unit 10 can suppress the fluctuation of the output light level as described above even at the time t1 that is substantially difficult to follow with the level adjustment function alone in the OADM unit 20, the optical transmission device 1 Even when the number of wavelengths fluctuates particularly greatly, the influence of the above-described SHB or the like on the output optical power can be minimized.
When the conventional optical transmission devices are connected in multiple stages so as to have the target transmission span number, the optical level fluctuation amount of the signal light transmitted through the span number (in this case, the fluctuation amount to the decrease side) May deviate from the allowable reception range at the signal receiving end (see reference numeral 131 in FIG. 16), for example, as shown in FIG. However, if the optical transmission device of the present embodiment is connected so as to have the above-mentioned target transmission span number, the output optical power fluctuation per optical amplification unit 10 can be suppressed more than the optical amplification unit of the prior art. For example, as shown in FIG. 6A, the signal can be kept within the allowable reception range at the signal receiving end (see reference numeral 131 in FIG. 16).

As described above, according to an embodiment of the present invention, the wavelength number information acquisition unit 16 and the calculation unit 17 as the target gain calculation unit cause a change in the signal light level, in particular, a change in the wavelength number of the wavelength multiplexed signal light. Since fluctuations in the output optical power of the optical amplifier can be suppressed at high speed, there is an advantage that the optical amplifier can be further multistaged and the transmission distance can be increased.
[B] Others Regardless of the embodiment described above, various modifications can be made without departing from the spirit of the present invention.

For example, in the above-described embodiment, the target gain for which the constant gain control is performed by the control signal output unit 18 is the target gain calculated by the calculation unit 17, but according to the present invention, AGC control is assumed. Even in such a control mode, it is possible to output a control signal to the EDFA 11 so as to obtain the target gain of AGC control calculated by the calculation unit 17.
In this embodiment, an EDFA using an erbium-doped optical fiber (EDF) as an amplification medium is applied as an optical amplifier. However, according to the present invention, an optical amplifier having another configuration may be applied.

Furthermore, according to the present embodiment, the optical transmission device 1 is provided with both the preamplifier 10a and the postamplifier 10b, but at least one of these preamplifiers and postamplifiers is provided. It is possible to provide the configuration as the optical amplification unit 10 of the present embodiment.
Furthermore, in the above-described embodiment, the wavelength number information acquisition unit 16 acquires the wavelength number information. However, according to the present invention, the wavelength number information acquisition unit 16 does not acquire the wavelength number information, but is input. When the number of wavelengths of the wavelength multiplexed signal light is larger than the preset threshold value S or greater than or equal to the threshold value S, a substantially constant gain value is calculated as the target gain of the optical amplifier, while the wavelength multiplexed signal light When the number of wavelengths is equal to or smaller than the threshold value S or smaller than the threshold value S, by using a function that calculates a value obtained by increasing or decreasing the gain value of the signal light according to the number of wavelengths as the target gain of the optical amplifier. The target gain may be calculated.

Furthermore, it is desirable to apply the present invention to individual optical amplifiers arranged at each node and compensate for output fluctuations occurring at each node for each node. However, the number of optical amplifiers to which the present invention is applied, the optical amplifiers The type is not limited.
Moreover, it is possible for those skilled in the art to manufacture the apparatus of the present invention based on the disclosure of the above-described embodiment.

[C] Appendix (Appendix 1)
An apparatus for controlling the gain of an optical amplifier for amplifying input wavelength multiplexed signal light,
A target gain calculator that calculates a target gain so that the gain (output) of the signal light increases or decreases as the number of wavelengths of the wavelength multiplexed signal light decreases;
And a control signal output unit for outputting a control signal to the optical amplifier to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculation unit. apparatus.

(Appendix 2)
The gain control apparatus according to claim 1, wherein the rate of change of the gain (output) of the signal light with respect to the number of signal wavelengths changes steeply and continuously as the number of signal wavelengths decreases.
(Appendix 3)
An apparatus for controlling the gain of an optical amplifier for amplifying input wavelength multiplexed signal light,
When the number of wavelengths of the wavelength multiplexed signal light is greater than or equal to a preset threshold value, a substantially constant gain value is calculated as a target gain of the optical amplifier, while the wavelength multiplexed signal light When the number of wavelengths is equal to or less than the threshold value or smaller than the threshold value, a target gain that calculates a value obtained by increasing or decreasing the gain value (output value) of the signal light according to the number of wavelengths as the target gain of the optical amplifier. A calculation unit;
And a control signal output unit for outputting a control signal to the optical amplifier to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculation unit. apparatus.

(Appendix 4)
The gain control apparatus according to appendix 3, wherein the threshold is a number equal to or less than the number of wavelengths corresponding to 25% of the total number of wavelengths that can be transmitted as the wavelength multiplexed signal light in a wavelength division multiplexing optical transmission system.
(Appendix 5)
The target gain calculator
A wavelength number information acquisition unit for acquiring wavelength number information of the wavelength multiplexed signal light amplified by the optical amplifier;
Based on the wavelength number information acquired by the wavelength number information acquisition unit, a calculation unit that calculates the target gain in amplification in the optical amplifier;
The gain control device according to any one of appendices 1 to 4, wherein the gain control device is provided.

(Appendix 6)
The wavelength number information acquisition unit
A power monitor that monitors the power of each of the wavelength-specific signal lights that are input to or output from the optical amplifier is provided, and the wavelength multiplexing is performed based on the monitoring result of the power monitor. 6. The gain control apparatus according to any one of appendices 1 to 5, wherein information on the number of wavelengths of signal light is acquired.

(Appendix 7)
An input optical power monitor that monitors the optical power of the wavelength multiplexed signal light input to the optical amplifier, and an output optical power monitor that monitors the optical power of the wavelength multiplexed signal light output from the optical amplifier,
The control signal output unit performs automatic gain constant control of the optical amplifier with the target gain calculated by the target gain calculation unit based on the monitoring result from the input optical power monitor and the output optical power monitor. A gain control apparatus according to any one of appendices 1 to 6, wherein a control signal for output is output to the optical amplifier.

(Appendix 8)
A signal light processing unit that performs processing on signal light for each wavelength forming wavelength multiplexed signal light to be transmitted in the wavelength division multiplexing optical transmission system;
An optical amplifier provided at the front stage and / or the rear stage of the signal light processing unit, for amplifying the input wavelength-multiplexed signal light with pumping light;
A gain control unit for controlling the gain of the optical amplifier;
The gain controller
A target gain calculation unit that calculates a value obtained by increasing or decreasing the gain (output) of the signal light as the number of wavelengths of the wavelength-multiplexed signal light is increased or decreased;
And a control signal output unit for outputting a control signal to the optical amplifier to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculation unit. apparatus.

(Appendix 9)
The optical transmission apparatus according to appendix 8, wherein the rate of change of the gain (output) of the signal light with respect to the number of signal wavelengths changes steeply and continuously as the number of signal wavelengths decreases.
(Appendix 10)
A signal light processing unit that performs processing on signal light for each wavelength forming wavelength multiplexed signal light to be transmitted in the wavelength division multiplexing optical transmission system;
An optical amplifier provided at the front stage and / or the rear stage of the signal light processing unit, for amplifying the input wavelength-multiplexed signal light with pumping light;
A gain control unit for controlling the gain of the optical amplifier;
The gain controller
When the number of wavelengths of the wavelength multiplexed signal light is larger than a preset threshold value or more than the threshold value, a substantially constant gain value is calculated as a target gain of the optical amplifier, while the wavelength multiplexed signal light When the number of wavelengths is equal to or less than the threshold value or smaller than the threshold value, target gain calculation for calculating a value obtained by increasing or decreasing the gain value from the constant gain value according to the wavelength number as the target gain of the optical amplifier And
And a control signal output unit for outputting a control signal to the optical amplifier to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculation unit. apparatus.

(Appendix 11)
The signal light processing unit is configured to individually adjust power for the signal light for each wavelength,
The control signal output unit outputs the control signal to the optical amplifier in order to control the optical power of the wavelength multiplexed signal light to be transmitted in cooperation with the operation of the power adjustment in the signal light processing unit. The optical transmission device according to any one of appendices 8 to 10, characterized in that:

(Appendix 12)
The optical transmission device according to any one of appendices 8 to 11, wherein the signal light processing unit performs branching or insertion processing for each wavelength of the wavelength multiplexed signal light to be transmitted.
(Appendix 13)
The optical amplifier includes an amplification medium and an excitation light supply unit that supplies excitation light for exciting the amplification medium to the amplification medium. Optical transmission device.

(Appendix 14)
A control method for controlling an amplification gain of an optical amplifier that amplifies input wavelength-multiplexed signal light by pump light,
The value of gain (output) of signal light increased or decreased as the number of wavelengths of the wavelength multiplexed signal light is reduced, and calculated as a target gain of the optical amplifier,
A gain control method for an optical amplifier, comprising: outputting a control signal to the optical amplifier so as to amplify the wavelength multiplexed signal light with the calculated target gain.

(Appendix 15)
The optical amplifier gain control method according to claim 14, wherein the rate of change of the gain (output) of the signal light with respect to the number of signal wavelengths changes rapidly and continuously as the number of signal wavelengths decreases.
(Appendix 16)
A control method for controlling an amplification gain of an optical amplifier that amplifies input wavelength-multiplexed signal light by pump light,
When the number of wavelengths of the wavelength multiplexed signal light is greater than or equal to a preset threshold value, a substantially constant gain value is calculated as a target gain of the optical amplifier, while the wavelength multiplexed signal light When the number of wavelengths is equal to or less than the threshold value or smaller than the threshold value, a value obtained by increasing or decreasing the gain value from the constant gain value according to the number of wavelengths is calculated as a target gain of the optical amplifier,
A gain control method for an optical amplifier, comprising: outputting a control signal to the optical amplifier so as to amplify the wavelength multiplexed signal light with the calculated target gain.

(Appendix 17)
In the case where the number of wavelengths is equal to or less than the threshold value, or smaller than the threshold value,
When the output optical power of the wavelength multiplexed signal light output from the optical amplifier is smaller than a predetermined output optical power, a value increased according to the number of wavelengths from the constant gain value is set as the target gain. While calculating
When the output optical power of the wavelength multiplexed signal light output from the optical amplifier is larger than a predetermined output optical power, a value that is reduced from the constant gain value according to the number of wavelengths is set as the target gain. The gain control method for an optical amplifier according to appendix 16, wherein the gain control method is calculated.

(Appendix 18)
18. The optical amplifier according to appendix 16 or 17, wherein the threshold is a number equal to or less than the number of wavelengths corresponding to 25% of the total number of wavelengths that can be transmitted as the wavelength multiplexed signal light in a wavelength division multiplexing optical transmission system. Gain control method.
(Appendix 19)
When calculating the target gain,
Obtain wavelength number information of the wavelength multiplexed signal light,
19. The optical amplifier gain control method according to any one of appendices 14 to 18, wherein the target gain is calculated based on the acquired wavelength number information.

(Appendix 20)
14. A wavelength division multiplexing optical transmission system, wherein the optical transmission device according to any one of appendices 8 to 13 is connected via an optical transmission line.

It is a figure which shows the wavelength division multiplexing optical transmission system as one Embodiment of this invention. (A)-(D) are the figures for demonstrating the target gain of EDFA in one Embodiment of this invention. (A)-(C) are figures for demonstrating the operation | movement of this embodiment compared with the prior art. It is a flowchart for demonstrating operation | movement of one Embodiment of this invention. It is a figure which shows the specific example of a wavelength number fluctuation | variation. It is a figure for demonstrating the effect of one Embodiment of this invention. It is a block diagram which shows the structural example of a metro core system. It is a block diagram which shows the structural example of the conventional AGC amplifier. (A) And (B) is a figure for demonstrating the operation | movement at the time of the failure generation in the system shown in FIG. (A) And (B) is a figure for demonstrating the output optical power fluctuation | variation at the time of the wavelength number fluctuation | variation accompanying the failure generation in the system shown in FIG. It is a figure which shows an example of the amount of gain fluctuations of the wavelength dependence by SHB. (A) is a figure which shows an example of the gain change amount resulting from SHB with respect to a wavelength, (B) is an example which respectively shows an example of the gain change amount resulting from SRS with respect to a wavelength. It is a figure which shows an example of a Raman amplification band. It is a figure for demonstrating the Raman effect between signal wavelengths. It is a figure for demonstrating the subject of a prior art. It is a block diagram for demonstrating a signal receiving end.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical transmission apparatus 10 Optical amplifying part 10a, 102a Preliminary optical amplifying part 10b, 102b Rear optical amplifying part 11, 121 EDFA (optical amplifier)
12, 13, 122, 123 Optical branching unit 14, 15, 124, 125 Photodiode 16 Wavelength information acquisition unit 17 Calculation unit 18 Control signal output unit 19 Gain control unit 20, 101 OADM unit 100, 100A to 100C OADM node 110 Optical transmission line 120 AGC amplifier 126 Constant gain control unit 131 Optical receiver 132 Optical transmitter

Claims (12)

An apparatus for controlling the gain of an optical amplifier for amplifying input wavelength multiplexed signal light,
When the number of wavelengths of the wavelength multiplexed signal light is equal to or less than a set threshold, the characteristics of the output optical power fluctuation of the optical amplifier is acquired in advance , and the change in the number of wavelengths based on the acquired characteristics of the output optical power fluctuation The value of the gain of the wavelength multiplexed signal light increases as the number of wavelengths of the wavelength multiplexed signal light decreases, or the wavelength multiplexed signal is reduced so that the amount of fluctuation of the output optical power due to A target gain calculation unit for calculating one of the values obtained by decreasing the gain of the wavelength multiplexed signal light as the number of wavelengths of light is reduced as a target gain of the optical amplifier;
And a control signal output unit for outputting a control signal to the optical amplifier to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculation unit. apparatus. In claim 1,
A gain control apparatus characterized in that the rate of change in gain of the wavelength multiplexed signal light with respect to the number of signal wavelengths changes steeply and continuously as the number of signal wavelengths decreases. An apparatus for controlling the gain of an optical amplifier for amplifying input wavelength multiplexed signal light,
When the number of wavelengths of the wavelength multiplexed signal light is larger than a set threshold,
While calculating a substantially constant gain value as the target gain of the optical amplifier,
When the number of wavelengths of the wavelength multiplexed signal light is less than the threshold,
When the number of wavelengths of the wavelength-multiplexed signal light is equal to or less than the threshold, the characteristics of the output optical power fluctuation of the optical amplifier is acquired in advance, based on the acquired characteristics of the output optical power fluctuation, the change due to the change in the number of wavelengths A value obtained by increasing the gain value of the wavelength multiplexed signal light in accordance with the number of wavelengths, or a wavelength multiplexed signal in accordance with the number of wavelengths, so that the amount of fluctuation of the output optical power is suppressed to the amount of fluctuation for compensating the characteristics. A target gain calculator that calculates one of the values obtained by reducing the gain value of light as the target gain of the optical amplifier;
And a control signal output unit for outputting a control signal to the optical amplifier to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculation unit. apparatus. The target gain calculator
A wavelength number information acquisition unit for acquiring wavelength number information of the wavelength multiplexed signal light amplified by the optical amplifier;
Based on the wavelength number information acquired by the wavelength number information acquisition unit, a calculation unit that calculates the target gain in amplification in the optical amplifier;
The gain control device according to claim 1, wherein the gain control device is provided. A signal light processing unit that performs power adjustment on the signal light for each wavelength forming the wavelength multiplexed signal light to be transmitted in the wavelength multiplexing optical transmission system;
An optical amplifier provided at the front stage and / or the rear stage of the signal light processing unit, for amplifying the input wavelength-multiplexed signal light with pump light;
A gain control unit for controlling the gain of the optical amplifier;
The gain controller
When the number of wavelengths of the wavelength multiplexed signal light is equal to or less than a set threshold, the characteristics of the output optical power fluctuation of the optical amplifier is acquired in advance , and the change in the number of wavelengths based on the acquired characteristics of the output optical power fluctuation The value of the gain of the wavelength multiplexed signal light increases as the number of wavelengths of the wavelength multiplexed signal light decreases, or the wavelength multiplexed signal is reduced so that the amount of fluctuation of the output optical power due to A target gain calculation unit for calculating, as the target gain of the optical amplifier, one of the values obtained by decreasing the gain of the wavelength multiplexed signal light as the number of wavelengths of light decreases;
And a control signal output unit for outputting a control signal to the optical amplifier to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculation unit. apparatus. In claim 5,
An optical transmission apparatus characterized in that the rate of change in gain and loss of wavelength multiplexed signal light with respect to the number of signal wavelengths changes steeply and continuously as the number of signal wavelengths decreases. The target gain calculator is
When the SN tolerance or the input lower limit tolerance of the optical receiver optically connected to the wavelength division multiplexing optical transmission system is lower than a preset first threshold value, the gain of the wavelength division multiplexed signal light decreases as the number of wavelengths decreases. When the input upper limit tolerance of the optical receiver is lower than a preset second threshold value, the gain of the wavelength multiplexed signal light decreases as the number of wavelengths decreases. The optical transmission device according to claim 5, wherein the optical transmission device is calculated as follows. A signal light processing unit that performs power adjustment on the signal light for each wavelength forming the wavelength multiplexed signal light to be transmitted in the wavelength multiplexing optical transmission system;
An optical amplifier provided at the front stage and / or the rear stage of the signal light processing unit, for amplifying the input wavelength-multiplexed signal light with pumping light;
A gain control unit for controlling the gain of the optical amplifier;
The gain controller
When the number of wavelengths of the wavelength multiplexed signal light is larger than a preset threshold,
While calculating a substantially constant gain value as the target gain of the optical amplifier,
When the number of wavelengths of the wavelength multiplexed signal light is less than the threshold,
When the number of wavelengths of the wavelength-multiplexed signal light is equal to or less than the threshold, the characteristics of the output optical power fluctuation of the optical amplifier is acquired in advance, based on the acquired characteristics of the output optical power fluctuation, the change due to the change in the number of wavelengths A value obtained by increasing the gain value of the wavelength multiplexed signal light in accordance with the number of wavelengths, or a wavelength multiplexed signal in accordance with the number of wavelengths, so that the amount of fluctuation of the output optical power is suppressed to the amount of fluctuation for compensating the characteristics. A target gain calculation unit for calculating one of the values obtained by reducing the gain value of light as the target gain of the optical amplifier;
And a control signal output unit for outputting a control signal to the optical amplifier to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculation unit. apparatus. A control method for controlling an amplification gain of an optical amplifier that amplifies input wavelength-multiplexed signal light by pump light,
When the number of wavelengths of the wavelength multiplexed signal light is less than or equal to a set threshold, to obtain in advance the characteristics of the output optical power fluctuation of the optical amplifier,
The number of wavelengths of the wavelength multiplexed signal light is small so that the fluctuation amount of the output optical power due to the change in the number of wavelengths is suppressed to the fluctuation amount that compensates the characteristic based on the acquired characteristic of the fluctuation of the output optical power. As the target gain of the optical amplifier, the value of the gain of the wavelength multiplexed signal light increased, or the value of the gain of the wavelength multiplexed signal light decreased as the number of wavelengths of the wavelength multiplexed signal light decreases,
A gain control method for an optical amplifier, comprising: outputting a control signal to the optical amplifier so as to amplify the wavelength multiplexed signal light with the calculated target gain.   10. The gain of an optical amplifier according to claim 9, wherein the rate of change in the gain of the wavelength multiplexed signal light with respect to the number of signal wavelengths changes rapidly and continuously as the number of signal wavelengths decreases. Control method. Calculating the target gain
When the SN tolerance or the input lower limit tolerance of the optical receiver optically connected to the wavelength division multiplexing optical transmission system is lower than a preset first threshold value, the gain of the wavelength division multiplexed signal light decreases as the number of wavelengths decreases. When the input upper limit tolerance of the optical receiver is lower than a preset second threshold value, the gain of the wavelength multiplexed signal light decreases as the number of wavelengths decreases. 11. The gain control method for an optical amplifier according to claim 9, further comprising calculating so as to be. A control method for controlling an amplification gain of an optical amplifier that amplifies input wavelength-multiplexed signal light by pump light,
When the number of wavelengths of the wavelength multiplexed signal light is larger than a preset threshold,
While calculating a substantially constant gain value as the target gain of the optical amplifier,
When the number of wavelengths of the wavelength multiplexed signal light is less than the threshold,
When the number of wavelengths of the wavelength multiplexed signal light is less than or equal to the threshold, the characteristics of the output optical power fluctuation of the optical amplifier is acquired in advance ,
Based on the obtained characteristics of the output light power fluctuation, the wavelength-division multiplexed signal light according to the number of wavelengths so that the amount of fluctuation of the output light power due to the change in the number of wavelengths is suppressed to the amount of fluctuation that compensates for the characteristics. A value obtained by increasing the gain value or a value obtained by decreasing the gain value of the wavelength multiplexed signal light according to the number of wavelengths, as a target gain of the optical amplifier,
A gain control method for an optical amplifier, comprising: outputting a control signal to the optical amplifier so as to amplify the wavelength multiplexed signal light with the calculated target gain.

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